Poor Arm Position May Significantly Skew BP Readings

Common arm positions for blood pressure (BP) measurements that stray from guidelines — arm in lap or hanging at side — led to substantial overestimation of hypertension in a study published in JAMA Internal Medicine. 

Guidelines for BP measurement recommend arm support on a desk with the midcuff at heart level. Overestimating BP can lead to unnecessary patient follow-up and overtreatment. Hypertension affects approximately 86 million adults in the United Statesand more than one billion people globally. 

This study has widespread implications given the number of settings where BP checks are performed and the growth in patients taking their own BP readings at home, said Donald DiPette, MD, who was not part of the research and was asked to comment on the findings. DiPette is the Distinguished Health Sciences Professor at the School of Medicine Columbia, University of South Carolina, Columbia.

Substantial Overestimation

In the crossover, randomized trial of 133 adults, Hairong Liu, MHS, with Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, and colleagues found that supporting the arm on the lap overestimated systolic BP (SBP) by 3.9 mm Hg and diastolic BP (DBP) by 4.0 mm Hg. When the arm hung at the side, readings overestimated SBP by 6.5 mm Hg and DBP by 4.4 mm Hg, with consistent results across subgroups.

Participants were randomly assigned to get a series of BP measurements with the arm positioned in three ways: Supported on a desk; hand supported on lap; and arm unsupported at the side. Because BP readings are intrinsically variable, all had a fourth set of BP measurements with the arm supported on a desk. 

Participants’ mean age was 57 years; 48 participants (36%) had SBP of ≥ 130 mm Hg; and 55 participants (41%) had a body mass index of ≥ 30.

Two researcher team staff members conducted all the measurements. They received standardized training and completed a certification test in BP measurement, administered by a study author. Measurements were taken from 9 am to 6 pm using a validated oscillometric BP device (ProBP 2000 Digital Blood Pressure Device, Welch Allyn). Only the right arms were used unless a specific condition was present, such as an open sore.

Study’s Design Sets It Apart

The authors wrote that the design of the study set this work apart. “Earlier studies have shown that unsupported or arm positioning below heart level can overestimate SBP by 4-23 mm Hg and DBP by 3-12 mm Hg,” they note. But the strength of this study is the randomized, crossover design, they write, “which is in contrast to the majority of published studies where the order of arm positions before seated BP measurement was not randomized or not clearly described.”

DiPette, who says, “I’ve given my career to understanding hypertension,” praised the design as well.

Randomization of which position patients were assigned to first was important because the first reading is often higher than subsequent readings, DiPette said.

“That makes sense as the person acclimatizes to the environment,” he explained. BP can even vary within the same reading, he noted.

Incorrect Readings for Many Reasons

Incorrect measures are common given the number of settings and number of providers and patients taking blood pressure even with training, certification in the method, and educational materials.

“We recommend taking a blood pressure in any possible setting you can. Because it’s that critical,” he said. “Most of the time it’s taken in busy primary care settings. The pressures are there. Most times it’s only one reading. It’s the medical environment of today.”

He noted that although this study finds overestimation, different arm positions not recommended by guidelines could potentially result in underestimation of hypertension. 

“I liken the BP measurement to a laboratory test that has clear treatment implications. We would want the BP measurement to have the same rigorous accuracy as a blood test or radiologic machine,” he said. 

DiPette said more education is needed for patients as well as providers as patients may be monitoring their own BP at home. Patients should also know they can ask for a measurement to be repeated, know the correct arm position recommended by guidelines, and the implications of incorrect readings, he said.

This study was supported by Resolve to Save Lives, which is funded by Bloomberg Philanthropies, the Bill and Melinda Gates Foundation, and Gates Philanthropy Partners, which is funded with support from the Chan Zuckerberg Foundation. 

Liu reported grants from Resolve to Save Lives outside the submitted work. Coauthor Kunihiro Matsushita, MD, PhD, reported grants from the National Institutes of Health and personal fees from Kowa Company, RhythmX AI, and Fukuda Denshi outside the submitted work. DiPette declared no relevant financial relationships. He was part of a leadership team that developed World Health Organization guidelines on hypertension. 

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, Northwestern magazine, and Nurse.com and was an editor at the Chicago Sun-Times, The Cincinnati Enquirer, and St. Cloud Times. Follow her on X@MLfrellick.